Although significant developments have been made in the field of drug delivery, concerns remain for drugs (for example, opioid analgesics) that are subject to abuse. Furthermore, the numbers of legitimate patients misusing such drugs, either deliberately or accidentally, represents a serious medical problem. In particular, patient risk can be heightened when controlled release formulations are used because larger amounts of the pharmaceutically active agent typically are incorporated into these formulations to facilitate reduced dosing-frequency. However, while controlled release formulations may offer greater convenience and an improved adverse event profile, serious problems can occur if the control release mechanism is compromised in any way, for example, by accidental chewing or grinding of, or other damage to, the tablet, or co-ingestion with alcohol. Under these scenarios, immediate release of the pharmaceutically active agent followed by rapid absorption of up to a total daily dose of the pharmaceutical agent can have potentially fatal consequences.
While a number of approaches have been tried to address the abuse and misuse of certain drugs, no effective approach has yet been commercialized. To date, the approaches employed include, for example, deterrent formulations, agonist/antagonist formulations, and prodrug formulations.
Deterrent formulations are formulations that contain a noxious substance, such as, capsaicin, an emetic, or niacin. The aim is to prevent deliberate abuse by inflicting a painful or otherwise unpleasant reaction should the formulation be crushed or otherwise damaged prior to ingestion. For example, U.S. Patent Publication Nos. 2003/0068370, 2003/0068392 and 2007/0020188 describe incorporation of aversive agents (e.g., a bitter agent, an irritant, or an emetic agent) into a dosage containing an opioid analgesic. The aversive agents discourage an abuser from tampering with the dosage form and thereafter inhaling or injecting the tampered dosage. The potential risk of such additives to the legitimate user who accidentally damages the tablet is not addressed by such formulations.
Antagonist formulations contain inhibitors (antagonists) of the therapeutic drug. When the formulation is crushed, the inhibitors are intended to prohibit or reverse the action of the pharmaceutically active agent thereby reducing or eliminating any benefit for non-medical use. For example, naloxone is combined with pentazocine (Talwin®, sold by Sanofi-Winthrop) to deter parenteral abuse of pentazocine. Naloxone is intended to block the binding of pentazocine to opioid receptors. Similarly, naloxone is added to a buprenorphine-containing formulation (Temgesic®, sold by Reckitt & Colman). It is understood, however, that this approach, can expose legitimate patients to unnecessary drugs, and can potentially inhibit effective therapy because the inhibitors may be released during normal passage through the gastrointestinal tract. These formulations also assume that effective inhibition can be achieved (i.e., that the bioavailability, pharmacokinetics and relative affinities of the agonist and antagonist can be matched so as to elicit effective inhibition in the intended recipient). U.S. Pat. Nos. 3,773,955 and 3,966,940, for example, describe formulations containing combinations of opioid agonists and antagonists, in which the antagonist does not block the therapeutic effect when the mixture is administered orally but blocks analgesia, euphoria or physical dependence when administered parenterally in a crushed form by an abuser.
Prodrug formulations rely on in vivo metabolic conversion of the prodrug into the active drug by enzymes found, for example, in the gastrointestinal tract. While these formulations may prevent euphoria via intravenous or nasal administration of the drug, they do not address the problems associated with potential intoxication (for example, alcohol intoxication) post oral administration.
Because of such limitations with existing technologies, there exists an ongoing need for misuse preventative, controlled release formulations that can reduce the risk of intentional abuse and accidental misuse of formulations containing a pharmaceutically active agent.